The following description of the background of the invention is provided simply as an aid in understanding the invention and is not admitted to describe or constitute prior art to the invention.
Insulin is a small peptide consisting of fifty-one amino acids in two chains, denoted the A chain and the B chain, linked by disulfide bridges between cysteine residues. Human insulin has a molar mass of about 5607.4 amu. The A chain has twenty one amino acids and the B chain has thirty amino acids.
Insulin is a hormone that is central to regulating fat and steroid metabolism in the body. When blood sugar levels rise following a meal, insulin is released into the bloodstream and allows for the transport of glucose from the circulation into cells.
A deficiency in insulin production or utilization results in diabetes mellitus. Insulin is often administered for the treatment of diabetes. Diabetes and its complications represent a major public health issue. Thus, quantitation of insulin in diabetic and pre-diabetic patient samples is important both as a diagnostic tool and for monitoring patient treatment.
Immunological techniques have been widely used for insulin quantitation (see, e.g., Manley, et al., Clin Chem., 2007, 53:922-32), and several mass spectrometric methods have been reported for detecting and/or quantitating insulin. See, e.g., Stocklin, R., et al., Diabetes 1997, 46:44-50 (reporting quantitation of insulin in serum samples by immunoaffinity chromatography-solid phase extraction-HPLC-single mass spectrometry); Darby, S. M., et al., J. Anal Toxicol 2001, 25:8-14 (reporting SPE-HPLC-MS quantitation of insulin in plasma at above physiological levels); Fierens, C., et al., Rapid Commun. Mass Spectrom. 2001, 15:1433-41 (reporting detection of insulin in water solutions by HPLC-(ESI) MS/MS); Magnes, C., et al., 52nd ASMS Conference, May 2004 (reporting quantitation of insulin in serum with high resolution/high accuracy mass spectrometry); Thevis, M., et al., Anal. Chem., 2005, 77:3579-85 (reporting immunoaffinity chromatography-solid phase extraction-HPLC-tandem mass spectrometric methods for quantitation of insulin and detection of insulin B-chain from plasma); Thevis, M., et al., Anal. Chem., 2006, 77:3579-85 and Thomas, A., et al., Anal. Chem., 2007, 79:2518-24 (reporting solid phase extraction-immunoaffinity chromatography-solid phase extraction-HPLC-tandem mass spectrometric methods for quantitation of insulin and detection of insulin B-chain from plasma); Uytfanghe, K., et al., Rapid Comm Mass Spectrom., 2007, 21:819-821 (reporting immunoaffinity chromatography-solid phase extraction-HPLC-tandem mass spectrometric methods for quantitation of insulin from serum); Rodríguez-Cabaleiro, D., et al., Clin Chem., 2007, 53:1462-69 (reporting immunoaffinity chromatography-solid phase extraction-HPLC-tandem mass spectrometric methods for quantitation of insulin and detection of insulin B-chain from plasma); Thevis, M., et al., Mass Spectrom. Reviews, 2008, 27:35-50 (reporting immunoaffinity chromatography-solid phase extraction-HPLC-tandem mass spectrometric methods for quantitation of insulin and detection of insulin B-chain from plasma); and Guedes, S., J. Am. Soc Mass Spectrom, 2009, 20:1319-26.